At the highest point, around the middle of the coaster track is one of the 200 Flying Rats.

The name 'Screamer' is likely a reference to a person who makes a lot of noise during sex (it is said that they are a 'screamer'). However, the name could also be a possible reference to people screaming on a roller-coaster.

Trivia

In the game manual of GTA IV, there's a section for the Screamer and it says, "Too bad you can't ride the Screamer because what would be better than riding a 100 year-old rollercoaster made out of wood?"

Although you technically cannot ride the Screamer, there are means of "riding" it with a car. The northern side of the coaster has a section that reaches the ground, and it has no railing, so the player can take a car and "ride" the Screamer.